Process and apparatus for making shaped cellular articles from expandable thermoplastic resins



8 5 6 8, 7 2R oOAS MN LI Ls EE GR C m1 PT As HA SL P3 GWG Lwnm M EKE Am n MM 5 E Mmmm 8 8. HSDD N .U d nunk RXi AEF wm AR DF NS Am S SC 7 EN 2 C om wm m 9 1 H 1 1 AMH .L E c T O 5 All? .a w l rl; i f /4/ 5 5 2 l f 2 /JNUL E 5' ENTRH/N AND FLOW )VH/LE HEAT/N61` RNULES MOL D l E VAGLIA TE D/SCHRGE 14R TIC L E FIG. I

INVENTOR. RICHARD H. [MME/ W FIG. 3

w/Mwk United States Patent O PRCESS AND APPARATUS FOR MAKING SHAPED CELLULAR ARTICLES FROM EX- PANDABLE THERMOPLASTIC RESINS Richard H. Immel, Sewickiey, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed Dee. 5, 1963, Ser. No. 328,305 11 Claims. (Cl. 264-51) This invention relates generally to a method of forming shaped articles from granules of a thermoplastic material and, more particularly, to the rapid forming of shaped cellular articles from expandable granules of a thermoplastic resin.

The making of low density cellular shaped plastic articles from expandable granules or beads of thermoplastic material is well-known. Such granules generally contain either a liquid which boils below the softening point of the thermoplastic material or a chemical, or possibly a combination of chemicals, which will evolve gas when the granules are heated 4to their softening point. These granules are placed in a mold cavity which defines the shape of the desired finished article. Steam or other suitable heating media is then injected under pressure into the mold cavity to heat the beads or granules labove their softening point and cause them to expand and completely fill the mold cavity and fuse together.

The foregoing process has worked well to produce a wide variety of articles. This process has disadvantages of being time consuming and when thick articles are made, great care must be exercised or a finished article of nonuniform density will result.

It has now been found that the tendency for the large density gradient existing in thick molded articles is due to the fact that as the heating medium is injected into the expandable beads from two or more sides of the mold cavity, the heat becomes concentrated in the center of the cavity causing the beads there to be heated to a higher temperature than the surrounding beads. Because of this, these beads tend to expand to a greater extent than those closer to the surface of the article. This effect is enhanced due to the fact that after the heating medium is cut off and the surface beads begin to cool, the center beads remain hot and continue to expand. This causes the central portion of an article of an average density of one pound per cubic foot to be as low as from 0.5 to

0.6 pound per cubic foot. Should the center of the article expand so that the density is less than .5 pound per cubic foot the center of the -article will be weakened to such an extent that collapse of the article is likely to occur on cooling and this is believed to be the limiting factor in attempting to produce articles of minimum density.

Heretofore, to prevent the expansion of the central beads from causing the whole article to bulge out of shape, the article had to be kept in the mold until the center became cool enough so that it would no longer expand. This is time consuming since heat transfer through the article is extremely slow which is, in fact, one ofthe properties which makes these articles useful, for example, for insulation.

In accordance with this invention, shaped foamed cellular plastic articles of uniform and extremely low density are rapidly prepared by entraining granules of an expandable thermoplastic material in a heated gaseous medium, whereby the granules are heated above the softening point but below the temperature where substantial expansion takes place as the granules are carried into a space that essentially defines the shape of said article, and thereafter subjecting said granules in said space to a vacuum so that said granules expand to ll the space and fuse together.

The novel process of this invention has the advantage 3,278,658 Patented Get. 11, 1966 ice that the time cycle for the molding operation is not dependent on the size and shape of the article to be formed. The beads in a heated condition enter the mold so no additional heating time is required. No substantial temperature gradient is encountered. As a result, the finished article prepared by the novel process of this invention has a uniform density throughout. Thus, articles having average density of as low as approximately .5-.6 pound per cubic foot can be molded without fear of collapse.

The .above and further objects and novel features of the invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

FIG. l is a flow diagram of the process,

FIG. 2 is a highly schematic vertical cross-section of an embodiment of the novel apparatus,

FIG. 3 is a vertical cross-section of the mold filling system with portions broken away.

The novel process of the invention for forming a shaped cellular plastic article is illustrated schematically by the iiow diagram of FIG. 1. The expandable polymeric granules are entrained in hot air. Then, the air and entrained granules are owed to the mold. During this flow, the expandable granules are heated to a temperature above the softening point of the thermoplastic material but below the temperature where substantial expansion takes place and beforer expansion occurs. In this condition, the particles enter the mold cavity that essentially defines the shape of the finished article. Thereafter, the granules are subjected to a vacuum whereupon the granules expand, coalesce, and fuse together to form a shaped foamed cellular mass. After the mass has cooled to a self sustaining surface temperature, it is removed from the mold as a finished article having a foamed structure of uniform density.

Mold 11 illustrated herein in FIG. 2 as having a substantially cubical shape is constructed as two sections. These are held in place in press 14 between platens 13 and 13. Platen 13 is fixed and platen 13 is movable toward and away from platen 13 by means of rod 15 which is actuated by cylinder 17, so that the mold can be opened and closed. Gasketed lands in mold 11 form an airtight seal where the halves of mold 11 come together.

Mold 11 has an outer solid metal shell 21 and an inner shell 23 of perforated or porous metal connected to outer shell 21 by mold lands 19. The inner shell defines a mold cavity 26 and the inner and outer shells define a chest 22.

Inner shell 23 contains imbedded coils 24 which are v connected to sources of steam and water through lines 25,

27 and 29 and connection 31 and liexible connection 33. The flow of steam is -controlled by valve 28 in line 27 and the flow of water is controlled by valve 30 in line 29. Coils 24 are connected to a drain liner 35 by connection 37 and flexible connection 39. Drain line 35 can be closed by valve 36.

Outer shell 21 has an inlet 41 for compressed air connected to a source of compressed air by means of line 43, said air being controlled by valve 45, and por-ts 47 connected to vacuum tank 49 by means of line 51, connection 53 and exible connection 55. Line 51 has a bleed line 57 for atmospheric air controlled by valve 59. Vacuum tank 49 can be isolated from mold 11 by closing valve 63 located in line 51 and is connected to a conventional vacuum source through line 61.

Inlet pipe 65 of blow ill gun 67, FIG. 3, passes through outer shell 21 to bead inlet `69 in inner Vshell 23. Aspirator 7'6 is connected to inlet pipe 65 of blow fill gun 67. Pipes 71 and 75 are connected to aspirator 76 so that a venturi chamber is formed at 78a. lPipe 71 is connected to a source of hot air under pressure and pipe 75 is connected to a heated container for granular polymeric material. Pipe 73 is connected to a source of cold air under pressure. Inlet pipe 65 is fitted with a piston 77 of suitable size and shape to close off bead inlet 69 which is actuated by a standard hydraulic ram 78, FIG. 2. The ow of air through lines 71, 73 and lines 8'1 and 83 of hydraulic ram 78 are controlled by conventional solenoid valves 82, 84, 86 and 88, FIG. 2.

A temperature sensing device 79 is located in pipe 65 opposite mold wall 21 and is connected to a temperature switch 80 which controls the operation of solenoid valves 82, 84, 86, 88 by conventional means well known in the art.

In practice, mold 11 is closed by platen 13 and rod 15 which is actuated by cylinder 17. Valve 36 on drain line 35 is closed and valve 28 to the steam supply which has a pressure of between 40 and 50 p.s.i.g. is Opened to ll coils 24 with steam and preheat inner mold shell 23 to between 200 and 230 F. Then valve 28 is closed and drain valve 36 is opened. Mold 11 is now in closed position. Hot air at a Itemperature of from 400 to 750 F. and a pressure of from 15 to 70 p.s.i.g. is delivered by line 71 to aspirator 76 of blow fill ygun 67 sucking granules through line 75 from a container heated from 150 to 170 F. The granules are entrained in the hot air and heated from to 10 F. above the softening point of the polymer but below the point at which substantial expansion of the granules occur while they are carried through pipe 65 to bead inlet 69 into mold cavity 26. The hot air is vented from cavity 26 through porous shell 23 `to chest 22 and out through connection-s 53 and 55 to bleed line 57 where it is vented to the atmosphere, valve 59 .being opened and valve 63 being closed. When mold cavity 26 becomes lled, back pressure is created in pipe 65 causing the air temperature to rise which i-s sensed by temperature sensor 79 connected to temperature switch 80. Temperature switch 80 activates valve 82 closing off hot air line 71, and activates valve 84 opening cold air line 73 to deliver air at a pressure of from 20-30 p.s.i..g. and at a tcmperature of 70-85 F. for several seconds to blow the excess beads in pipe 65 back through pipe 75 to the bead container and to cool pipe 65 so that the beads around bead inlet 69 are not scorched by `the rapid rise in temperature. Valve 88 on line 81 of hydraulic ram 78 is then activated causing piston 77 .to close bead inlet 69. When bead inlet 69 is closed, valve 59 on atmospheric bleed line 57 is closed and valve 63 in pipe 51 leading to vacuum tank 49 is opened causing a sudden vacuum of from 28 to 30 inches of mercury inside mold 11 which results in expansion and fusion of the beads in mold cavity 26 to conform to the shape of mold shell 23. Valve 63 is then closed and valve 59 opened t0 allow the mold to return to atmospheric pressure. Drain valve 36 is opened and water valve 30 is opened to circulate water at a temperature of from 40 to 50 F. to coils 24 and cool inner shell 23 to a temperature of 150 to 180 F. Rod 15 is then actuated by cylinder 17 to open mold 11. Valve 45 in ejection air line 43 is opened so that the air pressure causes the finished article to be ejected from mold shell 23.

Either virgin polymer beads (beads which have not bee expanded), or preexpanded beads (beads which have been partially expanded as, for example, described in United Sta-tes Patent No. 3,023,175) advantageously are placed in a storage container maintained at a temperature of from 140 to 170 F. so that they can be quickly heated -to fusion temperature while being carried into the mold by the hot air. The hot air is delivered to the venturi section of the blow fill gun under a pressure of from to 70 p.s.i.g. asA necessary depending on .the efliciency of the venturi. The temperature required for the compressed hot air will depend upon its pressure since the temperature will drop adiabatically with the sudden pressure drop when the air enters the venturi section. The pressure will drop .to from atmospheric pressure to 3 p.s.i.g., the higher pressure being due to back pressure from the mold cavity. The temperature of the compressed hot air is adjusted to heat the polymer beads being carried into the mold to a temperature of from 5-10 above their softening point. A compressed hot air temperature of 400 F. at pressure of 15 p.s.i.g. will `give a hot air blow gun discharge temperature of approximately 270-300 F. at a pressure of l to 3 p.s.i.g. which is suicient to heat the polymer beads to between 190 and 210 F. It has been found that at a hot air pressure of 70 p.s.i.g., a hot air temperature source of 750 F. is necessary to achieve a hot air blow fill gun discharge temperature of 300 F. at 3 p.s.i.g. One skilled in the art can read-ily determine at hot air pressures of between 15 and 70 p.s.i.g., the appropriate air temperature to give the desired blow gun discharge temperature blow .gun discharge temperatures generally range from Z50-350 F. A vacuum may be drawn during the mold filling operation to maintain the back pressure from 1 to 3 p.s.i.g.

The molding process is carried out at or below atmospheric pressure, so little pressure is needed to keep the mold closed and lightweight presses can be used. In practice, the closure pressure need not exceed about 5 p.s.i.g. This is advantageous, of course, as the mold itself can be constructed of lightweight materials.

The heating of inner shell 23 is option-al, its function being to give a smooth surface on the finished article. Vacuum tank 49 should maintain a vacuum in the mold cav-ity of from 15-30 inches of mercury when the vacuum is drawn on the mold.

EXAMPLE I Two halves of the mold were assembled in the press as indicate-d in FIG. 1 and the two halves brought together defining an inner mold cavity of approximately 11 x 11 x 11 inches. As the mold halves were closed, the walls of the mold cavity were heated by passing steam at 45 p.s.i.g. Ithrough the coils in the mold :shell so that the shell was heated to a temperature from 215 to 220 F. Hot air at a pressure of 40 p.s.i.g. and a temperature of 600 F. was delivered to the blow ll gun aspirator where the pressure dropped to from 1 to 3 p.s.i.g. causing a corresponding temperature drop to from 270 F. to 300 F. The air passing through the venturi of the blow fill gun drew preexpanded 1 p.c.f.) polystyrene beads, sold under the trademark Dylite F-40, which `had been preheated in the container to a temperature of to 155 F. from the bead containe-r. The entrained beads were heated by the hot air to a temperature of 202 to 208 F. as they were carried into the mold cavity by the hot air `which escaped through the holes in the porous inner shell and was vented to the atmosphere through the bleed line. When the mold cavity was filled, which took approximately 10 seconds, the temperature switch was actuated yby the temperature sensor. The switch shut off the hot air, turned on cold air which was iat a pressure of 25 p.s.i.g. and which had a temperature of 80 F. to clear and cool the bead inlet passage, and thereafter actuated the piston which closed the bead inlet to the mold cavity. At this time the bleed valve was closed and the valve to the vacuum tank was opened so that the pressure in the mold cavity dropped almost instantaneously to between 2 and 4 inches of mercury causing the beads to expand and fuse. After approximately 5 seconds, the valve to the vacuum tank was closed and the bleed valve opened to allow the mold cavity to return to atmospheric pressure. This step took approximately 4 seconds. Cooling Water at a temperature iof 48 to 50 F. was passed through the coil-s in the mold shell so that the shell wall was cooled to a temperature from to 165 F. After approximately 10 seconds from the time the mold was returned to atmospheric pressure the mold was opened and the molded block ejected. The block had a uniform density of about 1.0 p.c.f.

T-o illustrate the uniform density of the molded article, a one inch square core was taken through the block running from the center of one face to the center of the opposite face and comp-ared with a similar core taken from 6 EXAMPLE 111 A comparison of typical mold cycle times for the novel process of this invention carried out in accordance with the procedure of Example I as contrasted with the cona block molded by a conventional steam molding techniqu The Outer M portions were Cut away to partially ventional steam injection process u-sed heretofore is illuseliminate the effects due `to surface compression of the Hated below m Table H' beads from the comparison. Table Il Table l 10 VACUUM FUSION PROCESS [Typical time cycles. (1.0 pcf. preexpanded polystyrene beads)] Density of Density of Vacuum Conventional Block Formed Block Formed Operation Process, Steam Injec- 1% Inch Inerements From Top to in Example by Steam Seconds tion Process,

Bottom I (pcf.) Molding (pcf.) Seconds 1.16 1. 36 Close Mold 5 5 .96 1. 14 Preheat (l) 2o .95 .78 Mold Fili.-. 10 10 96 67 Fusion 5 15 1. 02 84 Return to Atmos here 5 1.04 1.18 Cooling 0-15 600 1.18 1. 27 Open and Eject. 5 5

Average 1.04 1.03 Total Time 30-45 655 l Preheating done during mold closing.

As can be seen from the table the density of the center increment (4) of the core taken from the block formed As can bij Seen from the tab1e-c0ns1der-ab1e savmfgs m in Example I is only 0 08 p c f less than the average time are achieved since the preheating step 1s accomplished density of the core (1.04 p.c.f.) and the maximum variad urmg the m01@ flosmg operano and the coohng Cyfle tion in density between increments 2 to 6 is likewise only time 1S either eliminated or greatly reduced. The molding 0.08 p.c.f. In comparison the ydensity of thev center in- O Pefatlons aCCOIUPllSlled 1n only 5 to 7 per cent of the Crement (4) of the Core taken from the block formed by time required by the conventional steam injection process. the steam molding process is 0.36 p.c.f. less than the EXPaPdable P01ymCfS-Sl11tahle fOr use in making cellular average density (1.03 pcf.) of the core and the maXi articles in accordance With this invention include a variety mum variation in density between increments 2 t-o 6 is of homopqlymef? and COlJOlS/ mers derived from vinyl 0.51 pcf. The end increments l and 7, whose density monomers Including styrene Vmyl Chloflde dlvmyl ben is still subject to surface effects even after eliminating 1A Zne alphamethyl Styrene, nuclear dlmethyl Styl-emes i inch on each end of the core, show considerably less varia- Vmyl naphthalene etc' artlcular PG13/me. that are use' tion in density from the center increment in the block pi'eful are polystyrene and its copolymers W1h- Such mono' pared in Example I as compared with the .block prepared rners as butadiene, alpha-methyl styrene, divinyl benzene, by tha Sam molding process- 40 isobutylene and acrylonitrile. These expandable materials have incorporated therein as a propellant a volatile or- EXAMPLE H ganic fluid in an amount of from 3 to 35 parts by Weight up as D a 5 iiliairaieiilevgiiageOxepgigl/lrtl b7e5airocrtrtmg; 45 example, butane, p entane, hexane, heptane, cyclohexane Weight of styrene and 25 percent by Weight of acryloni or halogenatedcderivatives of methane and ethane which 1e which h d been preexpandd to a density of l boil below 95 C. Other suitable propellants include water or a combination of chemicals which will evolve a Plerenf fftld ljlncongega-gf tom gas such as carbon dioxide, water vapor or nitrogen when Fh l Th d g P u h -d to heated to a temperature at or below the softening p oint 1 665 gflgpehtnir at lpercllramapde @pres of the polymer, for example sodium bicarbonate and citric acid. Suf@ f )f 15 P-S-'g- Was deliveedto th? 310W ll gun Whch The practice of the invention permits shaped foarned f o mo e quic y regar ess o size an s ape. 55 t also has enhanced pioduct quality and permitted the 0i h2o; alf, tumeddolhhcfllgdal glch Ya/ at fpgulle fc rrnation of very `low density foamed articles without fear 0 1151-3- an 1 Pe fe 0 o collapse. Since the mechanical forces on the mold are .o to e presses are used as well as lightweight molds which has around the beaf Inlet, and acuatd the PlStOIl Whlch resulted in lower initial equipment costs. Other advanclosed the bead inlet to the mold cavity. The bleed valve tages result from .the fact that the process is completely W38 C10-Sed and the YalVe t0A the Vacuum tank Opened dry, resulting in a dry molded article. The invention also gflul 513; Plxsfste 5111 "fil I nOlglgO ld fVOPtO--Z IDChe-S elsily lends itsfelf to a orrpletely automated system from C Se Il S, Va e `0 C Vacuum t e ourin o vir in ea s into an ex nd r tank was shut off and vthe bleed valve opened permitting mor/E11 of agnishedgmolded ar.ti1e pa e to the re the niold cavity to return to atmospheric pressure. The I claim; cooling Water valve to the coils in the mold wall was 1. A method of forming a shaped foamed Cellular they. opened circulating water at 48-50" F. through the coils moplastic article comprising forming an entrainnient of for 12 seconds which reduced the mold Wall temperature 70 granules of an expandable thermoplastic material in a subto 160 F.-l65 F: after which the cooling water was stantially dry heated gaseous medium, flowing said entrainshut off and the drain valve opened. The press was then ment into a space that defines the shape of said article while opened and the finished molded bloch ejected from the heating said granules to a temperature above the softening mold. The block had a uniform density of l pound per point of the thermoplastic material but below the temperacubic foot. ture where substantial expansion takes place as the granules flow to said space, thereafter subjecting said granules in said space to a vacuum so that said granules expand and fuse together to form a cellular plastic article conforming to said space, and then removing the article from said S ace.

p2. A method of form-ing a shaped foamed cellular thermoplastic article from partially expanded granules of an expandable thermoplastic material comprising, flowing particles with a substantially dry heated gaseous medium into a space that defines the shape of said article so that said granules enter said space at a temperature above the softening point of the thermoplastic material but below the temperature where substantial expansion takes place, thereafter subjecting said granules in said space without further heating to a vacuum to expand yand fuse `said granules together to form said foamed cellular plastic article conforming to the shape of said space, and then removing the article from said space.

3. A method of forming a shaped formed cellular thermoplastic article comprising forming an entrainment of granules of an expandable thermoplastic material in a substantially dry heated gaseous media to heat said granules to a temperature above the softening point ofthe thermoplastic material but below the temperature where substantial expansion takes place fiowing said entrainment into a preheated space that defines the shape of said article whereby the granules enter said space in a heated condition and no substantial temperature gradient is encountered, thereafter, without additional heating, subjecting said granules in said space to a vacuum to expand `and fuse said granules together to form a cellular plastic article conforming to said space, and then removing the article from said space.

4. A method of forming a shaped foamed cellular thermoplastic article from partially expanded granules of an expandable thermoplastic material which comprises heating said granules by means of a substantially dry heated gaseous medium to a temperature above the softening point of the thermoplastic material but below the temperature where substantial expansion takes place while flowing said granules to a mold, and

subjecting said granules in said tmold to a vacuum to expand and fuse said granules to form said cellular thermoplastic article,

said process being characterized by the omission of further increase in temperature of the granules in said mold.

5. A method of forming a shaped foamed cellular thermoplastic article from granules of an expandable thermoplastic material which comprises heating said granules by `means of a substantially dry hea-ted gaseous medium to a temperature of from -l0 C. above the softening point of the thermoplastic material but below the temper-ature where substantial expansion takes place while flowing said granules to a mold, and

subjecting said granules in said mold to a vacuum of from l5 to 30 inches of mercury to expand and fuse said granules to form said cellular thermoplastic article,

said process being characterized by the omission of further increase in temperature of the granules in said mold.

6. Method of forming a shaped foamed cellular thermoplastic article comprising forming an entrainment of granules of an expandable thermoplastic material in hot air at a preheated temperature of from 250 to 350 F., flowing said entrainment into a space that denes the shape of said article whereby the granules and air exchange heat during the fiow to said space and said granules are heated t-o a temperature from 5 to 10 F. above the .softening point of the thermoplastic material thereafter subjecting said granules in said `space to a vacuum of to 30 inches of mercury so that said granules expand and fuse together to form a cellular plastic article `conforming to said space and then removing the article from said space.

7. An apparatus for forming a shaped, foamed, cellular plastic article comprising a mold having a cavity that essentially defines the shape of said article, transfer means for forming an entrainment of expandable granules of a thermoplastic material in a substantially dry heated gaseous medium and fiowing said entrainment into said mold whereby said granules in said entrainment are heated to a temperature above the softening point of said thermoplastic material but below the temperature where substantial expansion of said granules takes place as the granules flow to the mold, means for subjecting said granules in said mold to a vacuum so that said granules expand and fuse together to form a foamed article, and means for removing said article from said mold.

8. The apparatus of claim 1 wherein said mold is divided into two sections each of said sections comprising (a) a solid metal outer shell, said shell having lands capable of forming an air tight sea-l when said sections are brought together;

(b) a sintered metal inner shell shaped to define one par-t of a mold cavity connected in spaced relationship to said outer shell so as to define a chest between said inner shell and said outer shell;

(c) outlet means from said chest through said outer shell for connection to vacuum and atmospheric air lines;

(d) means embedded in the walls of said inner .shell for circulating cooling and heating media through said walls;

(e) inlet and outlet means for said cooling and heating media;

at least one of said sections comprising (a) inlet means for the passage of beads into the mold cavity formed when said sections are brought together;

(b) means for closing said inlet means when the mold is filled;

(c) inlet means for the passage of compressed air to eject the molded article from said section and means for opening Iand closing said mold by moving one of said sections relative to the other.

9. The apparatus of `claim 8 wherein said means for forming and flowing an entrainment of expandable granules of a thermoplastic material in a substantially dry heated gaseous medium into said mold is a blow fill gun comprising an aspirator containing as an integral part thereof a venturi chamber and having `a first inlet for the passage of said granules into said aspirator, a second inlet for the passage of hot air under pressure into said aspirator, `an outlet for a mixture of said granules and said air whereby said air under pressure passing through said venturi chamber sucks said granules through said first inlet into said aspirator and ejects said granules and said air from said outlet at a high velocity, vertically extending hollow connecting means for connecting said outlet with said mold cavity, inlet means in said connecting means for the passage of cold air under pressure whereby excess granules are removed from said connecting means and said aspirator when said mold cavity becomes filled with granules, closure means positioned in said connecting means for closing the inlet to said mold cavity when said cavity becomes filled with granules and temperature sensing means in said connecting means for activating control means for said hot air under pressure, said cold air under pressure, and said closure means whereby the filling of said mold, the removal of the excess beads from said connecting means and said aspirator, and the closing of said mold cavity occur in sequence. v

10. Apparatus for forming a shaped foamed cellular thermoplastic article comprising a mold having an internal configuration corresponding to that of the article, a means for subjecting said mold to vacuum, a supply source for granules of expandable thermoplastic material, a supply source for heated air, means connected with said supplies for entraining said granules in said air and means for flowing the granu-les to said mold, a temperature sensor for responding to the temperature of said entrainment when said mold is lled with said granules and connected to means for stopping the ow of said entranment.

11. Apparatus for forming a shaped foamed cellular thermoplastic article comprising a mold having an internal conguration corresponding to that of the article, a means for subjecting said mold -to vacuum and means for forming an entrainmen-t of granules of expandable thermoplastic material in hot air and flowing said entrainment to the mold comprising a conduit leading to said mold, an aspirator for introducing said granules into said conduit, a source of hot air, means connecting said source of hot air to said aspirator for Ithe operation thereof, a temperature sensor responsive to the temperature of said entrainment of beads in air effected by said aspirator, and means responsive to said temperature -sensor for stopping the ow of air and beads to said mold, said last named means including a valve for stopping the ow `of hot air to said l10 aspirator, a piston in said conduit, and means to drive said piston in a direction to close said conduit when the mold is filled with granules.

References Cited by the Examiner ALEXANDER H. BRODMERKEL, Primary Examiner.

P. E. ANDERSON, Assistant Examiner.

UNITED STATES :PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,278 ,658 October ll 1966 Richard H. Immel rtifed that error appears in the above numbered pat- It is hereby ce and that the said Letters Patent should read as ent requiring correction corrected below.

line 67, after Column 7, line 66, Strike out "preheated"; "a" insert preheated Column 8, line I5, for the claim reference numeral "l" read 7 Signed and Sealed this 29th day of August 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attest-ing Ofr Commissioner of Patents 

1. A METHOD OF FORMING A SHAPED FOAMED CELLULAR THERMOPLASTIC ARTICLE COMPRISING FORMING AN ENTRAINMENT OF GRANULES OF AN EXPANDABLE THERMOPLASTIC MATERIAL IN A SUBSTANTIALLY DRY HEATED GASEOUS MEDIUM, FLOWING SAID ENTRAINMENT INTO A SPACED THAT DEFINES THE SHAPE OF SAID ARTICLE WHILE HEATING SAID GRANULES TO A TEMPERATURE ABOVE THE SOFTENING POINT OF THE THERMOPLASTIC MATERIAL BUT BELOW THE TEMPERATURE WHERE SUBSTANTIAL EXPANSION TAKES PLACE AS THE GRANULES FLOW TO SAID SPACE, THEREAFTER SUBJECTING SAID GRANULES IN SAID SPACE TO A VACUUM SO THAT SAID GRANULES EXPAND AND FUSE TOGETHER TO FORM A CELLULAR PLASTIC ARTICLE CONFORMING TO SAID SPACE, AND THEN REMOVING THE ARTICLE FROM SAID SPACE. 